The present invention relates to apparatuses and methods to measure three-dimensional data, namely to measure not only length and width of objects but also their height as well as their relative distance to the observer.
Humans use two eyes to measure three-dimensional (3-D) objects, for instance length, width and the third dimensionxe2x80x94height. This third dimension can also be referred to as distance away from the viewer.
This invention presents a novel apparatus and method to measure 3-D data of length, width and height. For the purpose of this invention, the term height and distance can be used interchangeably.
In order to make the field of the invention more readily understandable the following general remarks are provided with respect to the following known apparatuses and methods to measure 3-D data:
1. Stereoscopic Vision
2. Depth from Focus
3. Laser Range Finding
4. Structured lighting
1. Stereoscopic Vision
It is well known that the measurement of two dimensions (2-D) can be performed with one eye or one view. To measure the third dimension, a second eye or a second view is required. However, a single eye can produce two or more views if the eye is moved in a corresponding position for each view or if the object is moved in position relative to the eye.
In general, numerous devices are available to measure the third dimension using the methodology of stereo vision or stereopsis. FIG. 1 shows a conventional solution using two imaging devices 1 (for instance two video cameras 2 and lenses 3) where in the paths along which the rays of light have travelled during image formation are non-parallel due to the use of conventional lenses and wherein two images of the object to be observed (one in each camera) are generated.
FIG. 2 shows another conventional solution using a single video camera 2 and lens 3 used in conjunction with a set of mirrors or prismatic mirrors 4. Again, the paths along which the rays of light travel during image formation are non-parallel. Once again, this leads to the creation of two images within the single video camera 2.
However, the known methods as explained in conjunction with FIGS. 1 and 2 which makes use of non-parallel light rays for generating at least two images of the object to be viewed are relatively complex and bulky due the number of individual components used and the space that has to be provided for the travelling non-parallel light rays.
2. Depth from Focus
It is also possible to measure the third dimension by using a single view from a single imaging sensor. This is for example performed by using an optical imaging system, for instance a microscope, with an extremely narrow depth of field. The microscope is mounted vertically on a calibrated stand. To measure the height (z-axis), the microscope is moved up and down until the point of interest is in focus. The height data on the calibrated stand provides the height measurement. Multiple points can be measured in this way. However the disadvantage of this method is the slow speed in taking measurements, as servo-mechanical means have to be used to focus the optical imaging system from one point to next. Further details may be found in FIG. 3 in which a camera 2 is shown with a lens 3 having an extremely narrow depth of field. The camera 2 and the lens 3 may be moved up and downwards relative to an object to be observed along a calibrated stand 5 with a height meter 6 indicating the temporary position of the camera 2 and the lens 3. The distance of an object to be observed corresponds to the reading on the calibrated height meter 6 where the image of the object produced by the lens and camera is in focus, i.e. not blurred or otherwise distorted.
3. Range Finding
The third dimension of distance can also be obtained by using a pulsed or amplitude modulated wave or computing the phase changes in a transmitted and reflected wave. Laser, radar and ultrasound devices (so-called sonar devices) are examples of apparatus using this art. The measurement may be based on interferometry or echo detection techniques. These techniques require expensive and highly sophisticated opto-electronic apparatus comprising inter alia transmitters, wave guiding means and receivers for the travelling waves which are directed to and reflected back by objects to be observed.
4. Structured Lighting
Structured lighting involves the projection of a light pattern on the surface of an object to be viewed and viewing the reflected light from one or more different angels, or the study of shadows as produced by the projected light. A classical example of structured lighting is a sundial.
Examples of structured lighting include the projection of a point of light, a line or a grid onto the object surface from an angle and viewing the light pattern using a video camera from a different angle. The light projection and the camera are analogous to the use of two views.
In view of the disadvantages of the above mentioned prior art techniques it is an object of the present invention to provide in addition to the known apparatuses and methods for measuring 3-D data a simplified apparatus and a simplified method for measuring three-dimensional data.
In particular it is an object of the present invention to provide an apparatus and a method for measuring 3-D data in which only a single eye or a single view are needed.
Another object of the present invention is to provide an apparatus and a method for measuring 3-D data in which there is no need for a calibrated high-precision height meter indicating the temporary position of the viewing eye.
Another object of the present invention is to provide an apparatus and a method for measuring 3-D data in which there is no need for sophisticated opto-electronical apparatus.
Yet another object of the invention is to provide an apparatus and a method for measuring 3-D data in which analyzing 3-D data may be performed with a conventional computing machine such as a standard micro-processor based personal computer without the need for extremely high computational power required for performing highly complex and time consuming mathematical operations for extracting relevant 3-D object data such as length, width and height from image data provided by an imaging means.
These objects are accomplished by an apparatus according to independent apparatus claim 1 and a method according to independent method claim 2.
The dependent claims relate to further advantageous embodiments of the present invention.
The features and advantages of the present invention will be more readily apparent from the following detailed discussion of preferred embodiments in conjunction with the enclosed drawings: